1. Field of the Invention
The present invention relates to the field of medical devices, more specifically to medical devices intended to treat stenoses in the vascular system.
Balloon dilatation (angioplasty) is a common medical procedure mainly directed at revascularization of stenotic vessels by inserting a catheter having a dilatation balloon through the vascular system. The balloon is inflated inside a stenosed region in a blood vessel in order to apply radial pressure to the inner wall of the vessel and widen the stenosed region to enable better blood flow.
In many cases, the balloon dilatation procedure is immediately followed by a stenting procedure where a stent is placed to maintain vessel patency following the angioplasty. Failure of the angioplasty balloon to properly widen the stenotic vessel, however, may result in improper positioning of the stent in the blood vessel. If a drug-eluting stent is used, its effectiveness may be impaired by such improper positioning and the resulting restenosis rate may be higher. This is a result of several factors, including the presence of gaps between the stent and the vessel wall, calcified areas that were not treated properly by the balloon, and others.
Conventional balloon angioplasty suffers from a number of other shortcomings as well. In some cases the balloon dilatation procedure causes damage to the blood vessel due to aggressive balloon inflation that may stretch the diseased vessel beyond its elastic limits. Such over inflation may damage the vessel wall and lead to restenosis of the section that was stretched by the balloon. In other cases, slippage of the balloon during the dilatation procedure may occur. This may result in injury to the vessel wall surrounding the treated lesion. One procedure in which slippage is likely to happen is during treatment of in-stent restenosis, which at present is difficult to treat by angioplasty balloons. Fibrotic lesions are also hard to treat with conventional balloons, and elastic recoil is usually observed after treatment of these lesions. Many long lesions have fibrotic sections that are difficult to treat using angioplasty balloons.
An additional problem associated with balloon angioplasty treatment has been the “watermelon seed effect.” Angioplasty is carried out at very high pressures, typically up to twenty atmospheres or higher, and the radially outward pressure of the balloon can cause axial displacement of the balloon in a manner similar to squeezing a watermelon seed with the fingers. Such axial displacement, of course, reduces the effectiveness of balloon dilatation. Another problem with conventional angioplasty balloon design has been deflation of the balloon. Even after the inflation medium is removed from a balloon, the deflated configuration will have a width greater than the original folded configuration which was introduced to the vasculature. Such an increase in profile can make removal of the balloon difficult.
Atherectomy/Thrombectomy devices intended to remove plaque/thrombus material may also include a structure that expands in a lesion while the plaque/thrombus removal mechanism is within this structure. The removed material is either being stacked in the catheter or sucked out thru the catheter. When the procedure is done, the expandable structure is collapsed and the catheter removed. Foreign object removal devices usually include a basket structure that needs to be expanded to collect the object and then collapse for retrieval. Distal protection devices usually include a basket structure that support a mesh that needs to be expanded distal to the treated lesion to collect the loose objects and then collapse for retrieval.
These devices usually include an elastic metallic material that needs to be expanded in the vascular system to fulfill its task and afterwards collapse to a small diameter to facilitate retrieval. The transition between the collapsed (closed) configuration to the expanded (open) configuration can be done in two ways: the structure can be at a normally closed (collapsed) configuration in which force is applied to cause the structure to expand. In this case, the elastic recoil of the structure will cause it to collapse back to closed configuration when the expanding force ceases. The structure may also be at a normally open (expanded) configuration in which a constraining element is forced over it to hold it down for the collapsed configuration (for example a constraining tube). When this constraining element is removed the structure is free to expand to the expanded (open) configuration. The structure material may also be non elastic. In this case, the structure will need to be forced to transit between both collapsed and expanded configurations.
One problem associated with conventional angioplasty expansion systems is that the transition between the collapsed and expanded configurations involves significant rotational and axial reaction forces. These reaction forces are applied by the structure on the catheter as a result of the force applied by the catheter to expand or close the structure. Axial reaction forces are created due the foreshortening of the structure during expansion. Rotational reaction forces (torques) are created when a non longitudinal element is forced to expand/collapse. Since the catheters are usually less stiff than the structure, these reaction forces may cause the structure to not expand or collapse properly, or cause undesired deformation to the catheter itself.
To overcome at least some of these problems, U.S. Pat. No. 5,320,634 describes the addition of cutting blades to the balloon. The blades can cut the lesions as the balloon is inflated. U.S. Pat. No. 5,616,149 describes a similar method of attaching sharp cutting edges to the balloon. U.S. Patent Publication 2003/0032973 describes a stent-like structure having non-axial grips for securing an angioplasty balloon during inflation. U.S. Pat. No. 6,129,706 describes a balloon catheter having bumps on its outer surface. U.S. Pat. No. 6,394,995 describes a method of reducing the balloon profile to allow crossing of tight lesions. U.S. Patent Publication 2003/0153870 describes a balloon angioplasty catheter having a flexible elongate elements that create longitudinal channels in a lesion or stenosis.
While the use of angioplasty balloons having cutting blades has proved to be a significant advantage under many circumstances, the present cutting balloon designs and methods for their use continue to suffer from shortcomings. Most commercial cutting balloon designs, including those available from INTERVENTIONAL TECHNOLOGIES, INC., of San Diego, Calif., now owned by BOSTON SCIENTIFIC, of Natick, Mass., have relatively long, axially aligned blades carried on the outer surface of an angioplasty balloon. Typically, the blades are carried on a relatively rigid base directly attached to the outer balloon surface. The addition of such rigid, elongated blade structures makes the balloon itself quite stiff and limits the ability to introduce the balloon through torturous regions of the vasculature, particularly the smaller vessels within the coronary vasculature. Moreover, the cutting balloons can be difficult to deflate and collapse, making removal of the balloons from the vasculature more difficult than with corresponding angioplasty balloons which do not include cutting blades. Additionally, the axially oriented cuts imparted by such conventional cutting balloons do not always provide the improved dilatation and treatment of fibrotic lesions which would be desired.
For these reasons, it would be desirable to provide improved cutting balloon designs and methods for their use. In particular, it would be desirable to provide cutting balloons which are highly flexible over the length of the balloon structure, which readily permit deflation and facilitate removal from the vasculature, and which are effective in treating all forms of vascular stenoses, including but not limited to treatment of highly calcified plaque regions of diseased arteries, treatment of small vessels and/or vessel bifurcations that will not be stented, treatment of ostial lesions, and treatment of in-stent restenosis (ISR). Moreover, it would be desirable if such balloon structures and methods for their use could provide for improved anchoring of the balloon during dilatation of the stenosed region.
It would further be desirable to minimize the reaction forces applied by the external structure to the catheter, and at the same time be able to control the expansion of the expandable structure. It would also be desirable to adjust the compliance of the system in a predictable way without changing the materials or geometry of the expandable structure. At least some of these objectives will be met with the inventions described hereinafter.
2. Description of the Background Art
The following U.S. patents and printed publication relate to cutting balloons and balloon structures: U.S. Pat. Nos. 6,450,988; 6,425,882; 6,394,995; 6,355,013; 6,245,040; 6,210,392; 6,190,356; 6,129,706; 6,123,718; 5,891,090; 5,797,935; 5,779,698; 5,735,816; 5,624,433; 5,616,149; 5,545,132; 5,470,314; 5,320,634; 5,221,261; 5,196,024; and Published U.S. Patent Application 2003/0032973. Other U.S. patents of interest include U.S. Pat. Nos. 6,454,775; 5,100,423; 4,998,539; 4,969,458; and 4,921,984.